1. Technical Field
The present invention relates to a display device, and particularly, to an ultrathin, lightweight and flexible liquid crystal display device and a manufacturing method thereof.
2. Related Art
A so-called flat panel type display device, such as a liquid crystal display device or an organic EL display device, is configured of one substrate (an active matrix substrate or a TFT substrate), on which is formed a thin film transistor (TFT) circuit, and an opposite substrate or a sealing substrate, which holds a liquid crystal layer or an emitting layer between itself and the TFT layer. It is common that a glass material is used for these substrates. In particular, the TFT substrate requires a high temperature process in a TFT formation. Consequently, a glass substrate is used which is of an inexpensive material having a heat resistance and a low heat expansion coefficient. However, glass being fragile, there is a limitation in reducing a thickness of the substrate, posing an impediment to promoting a reduction in thickness and weight, and an increase in flexibility, of the display device.
FIG. 6 is a plan view of a heretofore known liquid crystal display device. Also, FIG. 7 is a sectional view taken along line X-X′ of FIG. 6. The liquid crystal display device shown in FIG. 6 is configured by sealing a liquid crystal LC between a principal surface of a thin film transistor substrate (a TFT substrate) SUB1, which is a first glass substrate, and a principal surface of an opposite substrate (a color filter substrate or a CF substrate) SUB2, which is a second glass substrate, and bonding the thin film transistor substrate SUB1 and the opposite substrate SUB2 together with a seal agent SL. Thin film transistors TFT, unshown pixel electrodes, and an unshown wiring system are formed on the principal surface of the thin transistor substrate SUB1. A color filter CF divided into segments by an unshown black matrix or, in a case of a TN type liquid crystal display device, opposite electrodes (not shown) are formed on the principal surface of the opposite substrate SUB2.
One edge of the opposite substrate SUB2 is slightly retracted from a corresponding edge of the thin film transistor substrate SUB1, exposing one portion of the principal surface of the thin film transistor substrate SUB1. A wiring connection portion TMA is formed in the exposed portion. A wiring substrate FPC is connected to the wiring connection portion TMA. The wiring substrate FPC is a so-called flexible printed substrate, and one extremity thereof is connected to the wiring connection portion TMA of the thin film transistor substrate SUB1, while the other extremity is connected to an external circuit.
As heretofore described, a semiconductor thin film for a thin film transistor circuit is formed on the thin film transistor substrate SUB1, but as a high temperature process is required in this formation step, a glass substrate is used as the substrate. For this reason, in order to bend the display device, it is necessary to make the glass substrate thin. However, as shown in JP-A-2005-115087, as there is a limitation in reducing a thickness of the glass substrate, there is also a limitation on a bending degree of the display device.
A flexible display device which can be freely bent cannot be made using the glass substrate. For this reason, as shown in JP-A-7-140451, the display device can be freely transformed by using a plastic substrate.
However, the plastic material having no heat resistance, it is hard to form a high performance semiconductor thin film, and it is difficult to use the plastic substrate as a TFT substrate to which is applied the high temperature process which forms the semiconductor film for the thin film transistor circuit.